Variable impedance having a rolling diaphragm seal



March l, 1965 R. B. DEMERn-T ETAL 3,238,483

VARIABLE IMPEDANCE HAVING A ROLLING DIAPHRAGM SEAL Filed March 2o. 196:5

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l l I mi I n JJ t g A N fh s gg i R2 :i/ N INVENTORS RAYMOND BDEMER/r'r@y JoH/v c. SPERO@ United States Patent O 3,238,483 VARIABLE IMPEDANCEHAVING A ROLLING DIAPHRAGM SEAL Raymond B. Demeritt, Braintree, and JohnC. Sperou, Roxbury, Mass., assignors to Cambridge ThermionicCorporation, Cambridge, Mass., a corporation of Massachusetts Filed Mar.20, 1963, Ser. No. 266,639 7 Claims. (Cl. 336-136) The field of thisinvention is that of electrical impedance devices and more particularlythat of completely sealed, adjustably variable impedance apparatus.

In attempting to provide high quality tunable radio frequency impedancedevices which are effectively sealed against the entrance of .foreignmatter, including moisture, various configurations have been evolved.The most problematical source of diiiiculty encountered in the design ofsuch devices is the necessity of a sliding seal, at some pointyassociated with the adjusting means, compatible with electricalaccuracy and minimal dimensions. Whether of an axially sliding or arotating type, these seals are subject to wear and hence deteriorationof quality and eventual leakage, and they are further prone to admit oreven carry foreign matter through 4the seal during actual adjustment. lnorder to reduce these deciencies, it has been proposed to utilize sealsin the form of various conventional bellows and diaphragms by whichrelative movement can be introduced into a sealed space Without slidingcontacts. These devices however have disadvantages of their own, beingby their nature either limited in the range of adjustment available, orbulky in relation to the space available, or vulnerable at exposedsurfaces.

Objects of the present invention are to provide very compact tunableimpedance devices suitable for miniature type assemblies, in which theoperating parts are comple-tely sealed and which are accurate anadreliable in operation to a very high degree; to provide such deviceswhich reproducibly retain dimensional accuracy and remain stable whilesubjected to wide temperature and humidity variations as well asmechanical and electric shocks; to provide such devices which areadaptable to a broad range of circuitry requirements including a highreactance to resistance ratio, which .are well suited for incorporationin printed circuitry, and which are for such purposes electrically andmagnetically shielded and stable; to provide such devices whose.construction lends itself particularly well to guaranteed qualitycontrol and to the utilization of modern dielectric and magneticmaterials; and to provide such devices which, although of high qualityconstruction, are of relatively simple and inexpensive manufacture andassembly.

The substance and nature of the invention, for carrying out the aboveand related objects, may be summarized in some of its characteristicaspects as follows.

A first impedance element, such as a coil or capacitor In a practicallyimportant aspect an impedance device according to the invention includesa hollow, cylindrical, transversely divided housing, with the peripheralportion of the rolling diaphragm seal clamped between the two housingparts. The second impedance element is attached to a threaded stem whichis part of the movement, and

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the central portion of the rolling diaphragm seal is clamped between thesecond impedance element and the stem. A tuning nut held captive withinthe housing, and .accessible from an end of the housing, threadedlyengages the stem, and guide means prevent relative rotation of housingand nut, so that rotation of the nut axially adjusts the impedanceelements relative to each other. The movement or adjusting component islocated wholly without the seal-ed housing portion which contains onlythe impedance elements such that only a single nonrigid sealing element,the diaphragm, is necessary.

These and other objects, inventive aspects, and advantageous results ofthe invention will appear from the following detailed description ofpractical embodiments thereof illustrating its novel characteristics.

The description refers to .a drawing in which FIG. 1 is a longitudinalsection of a variable inductance device according to the invention;

FIG. 2 is a section on line 2-2 of FIG. l;

FIG. 3 is a section similar to FIG. l, of another embodiment of theinvention; and

FIG. 4 is a section on line 4 4 of FIG. 3.

The working parts of the device are contained within an elongate housing11 constructed in two hollow cylindrical parts, a first, impedancesleeve portion 12 and a second, movement sleeve portion 14, which twosleeve portions are adapted to be clamped together end to end as will bedescribed below. The sleeve 14 is externally threaded as shown at 13,for mounting the device through an opening of a panel or similarmounting device between .a nut (not shown) and the flange 16 of thesleeve 14, with a transverse face.

In the present embodiment, the impedance device chosen by way ofillustration is an inductor. A coil form 21 forms the first impedanceelement. It has at one end a ange 22 and at the other end a flanged head23 for mounting it on the sleeve 12. The head flange 23.1 has on theoutside a header 24 made of glass and providing a glass to metal sealwith the metal ring 25 and the pins 26 and 27. The coil is indicated at31 and, as shown at 32 and 33, the ends of the coil are joined with theinner ends of the terminal pins 26 and 27. The pins reach throughperforations 34, 35 of the coil form head 23 through which they areinserted prior to joining them with the coil leads. After having beenassembled separately, the coil form 21 with the coil 31, the header 24with ring 25, and the pins 26, 27, is secured to the housing sleeve 12by swaging a lip 38 of this sleeve over the metal ring 25. Afterswaging, the lip is soldered to the metal ring as indicated at 39,thereby hermetically sealing this end of the impedance sleeve 12 whichforms one portion of the housing as a whole.

The adjustable cup core component 41 of the inductor constitutes thesecond impedance element and consists of a cup-shaped outer portion 42having a central core 43. The cup core 41 is preferably made of powderediron and isk rigidly attached to a spindle 44 by way of a knurled stud45 molded thereinto. The spindle has two stepped collars 45.1, 45.2 anda llange 46, a neck being formed between the collar 45.1 and the flange46. Opposite the knurled part 45 a threaded shaft 48 extends from thelarger collar 45.2 of the spindle 44.

A metal tuning stem 51 has at one end a disc 52 with a rim 53 reachingbeyond the closed end of the lcup-core 41, and a perforation 5S which ispartly threaded as shown at 56 and which leads into an enlarged bore 57clearing the collar 45.2. A metal washer 61 is conned between the flange46 and the large collar 45.2, the ange 46 preferably being formed byswaging the edge of the smaller collar 45.1 over the washer 61. Thewasher 61 rests in a recess 62 of the powdered iron cup 41, reinforcingthe relatively fragile material of the cup itself on this face. It willbe understood that the washer 61 could be a fiange that is integral withthe spindle 45. The tuning stem has an outside thread 58 and a slot 74for a screwdriver.

Between the movement sleeve 14 and the tuning stem 51 is inserted atuning nut 71 which is held captive within the movement sleeve 14 byswaging a portion 72, integral with the movement sleeve, over a taper72.1 of the closed end of the nut 71. At the opposite open end, the rimof the nut rests against an inwardly extending annular ridge 14.1 of themovement sleeve 14, within a recess 14.2 of the ridge. The swaged tbetween the rim 72 of the movement sleeve and the tapered portion 72.1of the nut 71 is sufficiently loose to permit rotation of the nut withinthe movement sleeve without permitting longitudinal movementtherebetween. The closed end of the nut has a slot 74 for inserting atool such as a screwdriver. At its open end the tuning nut has athreaded bore 76 which fits and engages the outside thread 58 of thetuning stem 51.

A pin 81, serving as a rotation preventing guide means, is at one,reduced, end 82 pressed into a bore of the disc 52 of the stem 51 andslides in an aperture 84 of the inside ridge 14.1 of the movement sleeve14. A washer 87 is swaged over the other end of the pin 81 for 'thepurpose to be described hereinbelow.

A rolling diaphragm 91 is provided as a seal between the impedancehousing and the movement housing. Seals of this type are formed fromrubberized fabric and are commercially available for example under thetrade designation Bellofram The edge 92 around the central opening ofthe seal 91 is clamped between the Washer 61 on the tuning cup core 41and the face of the ange 52 of the tuning stem 51. The peripheral rim 93of the seal is clamped between the anges and 16 of the impedance sleeveportion 12 constituting an impedance housing and the movement sleeveportion 14 constituting a movement housing, respectively. These flangesand the faces engaging the inner edge of the seal are preferably shapedto form concentric ridges to provide a better seal. The tuning cup core41 and the tuning stem 51 are assembled by means of the above describedthreads 48 and 56 and the slot 59 for engaging a screwdriver.

The flanges 15 and 16 are assembled and compressed to confine the outerrim or peripheral portion of the rolling diaphragm seal 91 by means ofswaging the rim or lip 16.1 of the flange 16 over the flange 15.

The operation of the above described device is as follows.

Rotation of the tuning nut 71, for example by means of a screwdriver inthe slot 74, causes longitudinal movement of the stem 51 which isprevented from rotation by the guide pin 81. The cup core 41 will movelongitudinally relatively to the coil form 21 with coil 31. The rollingdiaphragm 91 will transfer its cylindrical portion between the innersurface of sleeve 12 and the outer surface of cup 42 during adjustment.The cup 42 thus performs the functions of carrying the seal sleeve andof inductance variation. The rolling diaphragm, in addition to sealing,very effectively assists in preventing rotatory movement between thetuning portion and the movement. The extent of relative longitudinalmovement is limited by the washer 87 on the pin 81 which contacts atopposite sides the faces A and B of housing and nut, respectively, atthe ends of the travel. The relative movement of the cup core and thecoil adjusts the inductance in well known manner, and it will be notedthat the relative motion is pure translation without rotation, which iscommonly referred to as transverse tuning and is superior to other modesof tuning.

A modification of the` above described embodiment is shown in FIGS. 3and 4. In this embodiment the impedance housing and the tuningcomponents to the left of the rolling diaphragm 191 may be identicalwith those CFI described above with reference to FIGS. l and 2, whereasthe movement components are constructed as follows.

The tuning stem 151 is fastened to the core proper by means of athreaded stud 144. The rolling diaphragm 191 is clamped between thewasher 160 and the rimmed liange 152, by means of a nut 153. The stem151 has a flange 154 pressed against the nut 153 by means of the insidethread of the stem matching the thread of stud 144. The tuning nut 171has an inside thread 176 which engages the outside thread 158 of thestem 151. The stem 151 has two slots 161, 162 into which extend two ears163, 164 of the movement housing 114. A stop washer 165 is fastened tothe outer end of the stem 151 by means of a screw 166. The tuning nut171 is secured to the movement housing 114 by means of a swage over rim172, in the manner described above with reference to the rim 72 shown inFIG. l.

The operation of this embodiment is similar to that of the deviceaccording to FIGS. l and 2, as follows. Upon rotating the tuning nut 171by means of the screwdriver slot 174, the stem 151 is moved in axialdirection, with the fixed ears 163, 164 sliding in the axially movingslots 161, 162 of the stem 151 thereby moving the cup core in axialdirection without rotation. The inner surfaces of the washer 165 and ofthe flange 152 respectively, and the faces of the ears 163, 164 serve asstops in the manner described above with reference to the stop element87.

It will be noted that the above `described embodiments of the deviceaccording to the invention have several advantages, among others thefollowing especially important ones.

The space within the housing portion 12 containing the sensitiveelectrical components proper is completely hermetircally sealed by thesoldering at 39 and the rolling diaphragm 91 firmly clamped between thecorrugated flanges 15 and 16, and the washer 61 and the flange 52. Itwill be evident that these seals can be made with any desired degree ofcompleteness. It will be further noted that the sealing provisions donot in any way increase the overall dimensions of the entire device,which results in very compact exterior dimensioning of the device asawhole.

The cup -core 41 with outer shell 42 and inner core 43 fits looselywithin the impedance housing 12 which provides ample insulating spacebetween the core and the non-magnetic metal housing, the absence ofclose proximity of housing and core preventing a lowering the Q value ofthe impedance circuit due to eddy current losses. The insert-ion of theinsulating diaphragm over the cup core further promotes this favorableeffect. Also, since the tuning nut 71 fits the housing part 14 closelyand only rotates without longitudinal displacement, foreign particleslange enough to foul the engagement between the threads of nut 71 andthe stem 51 is with `certainty avoided, the outer portion of the nut'71, with the slot 74, completely closing the device on one side similarto the closing of the device on the other side by means of the header24- within the metal ring 25. The cup core 42 ,serves several purposes,namely for sh-ielding and favorable impedance regulation, as a plate towhich the center of the diaphragm 91 is attached, and as a piston forcarrying the diaphragm in all positions, including that when the core isfully extended over the coil as shown in dot and dash lines at 42.1. Aswell known, diaphragms of the Bellofram type should roll off a firmsupport similar to the side walls of the cup .core 41 in order to bepreserved in proper shape. The clearance between 12 and 42 is ample 4forproviding the convolution of the diaphragm which is recommended by themakers.

The coil and the core are so designed that the center core 43 iscompletely withdrawn from the coil 31 while still in engagement with thecoil form 21, which provides as wide a range of exact inductancevariation as possible.

The amply dimensioned and rigid stop and guidance components securelymaintain the above mentioned range of adjustment, provide the desirabletraverse tuning without rotation. The peripheral stiffness of thediaphragm enhances the traverse operation, in addition to its principalpurpose 4of sealing and auxiliary purpose of dielection between metalhousing and cup core.

It will be apparent that the sealing and movement features of the abovevdescribed embodiments can be applied to tunable capacitors, withanalogous advantages.

It should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

We claim:

1. A variable impedance device comprising:

elongate housing means having a sealed end and an open end;

a first impedance element attached to said housing means near saidsealed end, extending into the housing means and distanced therefrom toprovide a space between the outside of the impedance element and theinside of the housing means;

a second impedance element mounted on said housing means near` its otherend for axial displacement relatively thereto and having a portionextending into said space with its outside distanced from said inside ofthe housing means with clearance peripheral of said space; and

a rolling diaphragm attached at its periphery to said housing means atsaid open end, hav-ing an aperture attached to said second impedanceelement adjacent said open end of the housing means to seal bothimpedance elements within the housing means, and extending with itsrolling portion into said clearance permitting appreciable relativemovement of the two impedance elements.

2. Device according to claim 1 wherein said iirst impedance element hasan axial recess, and said second impedance element has a core member andan outer tube shaped member whose outer surface constitutes said outsideof the second impedance element, said axial recess accommodating saidcore member.

3. Device according to claim 1 wherein said housing means has a movementsleeve portion extending from said rolling diaphragm on the sideopposite to said impedance elements, and which device further comprises,within said movement sleeve portion and attached to said secondimpedance element, means for non-rotatory axial displacement of thesecond impedance element.

4. A variable impedance device comprising:

a first impedance element;

a irst tubular housing portion having at one end means for attachingsaid rst impedance element to extend into the housing portion and toseal said end, and having a second end;

a second tubular housing portion having one open end and having at theother end means including a transverse face for attaching it to saidsecond end of the iirst housing portion;

a second impedance element extending at one side into said rst housingportion through said second end and including a stem projecting from theother side into said second housing portion;

a rolling diaphragm having a central opening portion and a peripheralportion that is at said attaching means clamped between said second endof the rst housing portion and said transverse face of the secondhousing portion;

means for clamping said central opening portion of the rolling diaphragmbetween said other side of the second impedance element, and said stem;and

in said second housing portion means for axially adjusting said stemclosing said open end and accessible through said open end;

whereby the impedance means can be displaced and relatively to eachother while they are completely sealed by the diaphragm within saidfirst housing portion.

S. A variable inductor comprising:

a metallic housing including a tubular impedance sleeve and coaxialthereto a tubular movement sleeve, said sleeves each having a ange atadjacent, inner ends respectively, the impedance sleeve having aninwardly extending ridge near its outer end, and the movement sleevehaving an inwardly extending ridge near its flange with an aperturetherein;

a coil form assembly including an insulating tube having an open end anda closed end with flanges at each end respectively, an insulating headplate with contact pins leading therethrough and with a metal ringhermetically sealed to its periphery and to the outer end of saidimpedance sleeve, said closed end of the tube ange being confinedbetween the head plate and said impedance sleeve ridge and the pinsextending through the impedance sleeve ridge;

a coil mounted on said insulating tube and having ends joined to theinner ends of said pins within said impedance sleeve;

a magnetic cup core including an outer shielding cup and coaxiallyjoined to the bottom of the cup a center core, the space between cup andcore iitting said open end flange of said coil form tube, and said cupbeing dimensioned to provide a space between said shielding cup and theinside of said impedance sleeve;

a tuning stem assembly including a metallic stem having an outsidethread, a threaded central bore and a ange at one end, and a threadedstud fitting said central bore thread and having means for fastening itto said center core at the bottom of the cup core;

a centrally perforated rolling diaphragm clamped with its peripherybetween said anges of said impedance and movement sleeves, and with itscentral perforation clamped between said cup core bottom and said tuningstem flange by tightening said central bore of the tuning stem, on saidthreaded stud, the cylindrical portion of said diaphragm being capableof rolling on the outside of said shielding cup in said space betweensaid cup and said irnpedance housing;

a tuning nut having an open end with a threaded recess and a closed endwith a tapered edge engaged by the rim of said outer end of the movementsleeve swaged over said tapered edge, a shoulder near and facing awayfrom said closed end, said open end resting against said ridge of themovement sleeve, and said threaded recess engaging the outside thread ofsaid tuning stem; and

antirotation guide means including a guide pin fastened to said flangeof said tuning stem and fitting said aperture of said inwardly extendingridge of said movement sleeve, and at the end of the pin shoulder meansfor contacting the corresponding oppositely facing sides of saidmovement housing ridge and of said tuning nut shoulder.

6. Device according to claim 4 further including:

a guide pin fastened to said stem;

an inwardly extending projection of said second housing portion iittingsaid guide pin, for preventing relative rotary movement of said stem andsaid second impedance element;

opposite stop faces on said pin and said housing portion, respectively;and

two opposite stop faces at the end of said pin.

7. Device according to claim 4 further including:

a guide slot longitudinally of said stem,

a guide ear projecting from said second housing portion into said slot,for preventing relative rotary movement of said stem and said secondimpedance element, and

7 8 projections at opposite points of said slot on either side 3,082,7923/ 1963 Jenkins.

of said ear provldmg stops for sald ear. FOREIGN PATENTS ReferencesCited by the Examiner 1,010,182 6/ 1957 Germany.

UNITED STATES PATENTS 5 JOHN F. BURNS, Primary Examiner. 691,190 1/1902Sharp. 3,027,527 3/1962 West 336-136 X LARAMIE E ASKIN Exammer'3,043,338 7/1962 Hanson.

1. A VARIABLE IMPEDANCE DEVICE COMPRISING: ELONGATE HOUSING MEANS HAVINGA SEALED END AND AN OPEN END; A FIRST IMPEDANCE ELEMENT ATTACHED TO SAIDHOUSING MEANS NEAR SAID SEALED END, EXTENDING INTO THE HOUSING MEANS ANDDISTANCED THEREFROM TO PROVIDE A SPACE BETWEEN THE OUTSIDE OF THEIMPEDANCE ELEMENT AND THE INSIDE OF THE HOUSING MEANS; A SECONDIMPEDANCE ELEMENT MOUNTED ON SAID HOUSING MEANS NEAR ITS OTHER END FORAXIAL DISPLACEMENT RELATIVELY THERETO AND HAVING A PORTION EXTENDINGINTO SAID SPACE WITH ITS OUTSIDE DISTANCED FROM SAID INSIDE OF THEHOUSING MEANS WITH CLEARANCE PERIPHERAL OF SAID SPACE; AND A ROLLINGDIAPHARGM ATTACHED AT ITS PERIPHERY TO SAID HOUSING MEANS AT SAID OPENEND, HAVING AND APERTURE ATTACHED TO SAID SECOND IMPEDANCE ELEMENTADJACENT SAID OPEN END OF THE HOUSING MEANS TO SEAL BOTH IMPEDANCEELEMENTS WITHIN THE HOUSING MEANS, AND EXTENDING WITH ITS ROLLINGPORTION INTO SAID CLEARANCE PERMITTING APPRECIABLE RELATIVE MOVEMENT OFTHE TWO IMPEDANCE ELEMENTS.